In general, an accelerator is a device which uses an electromagnetic field to accelerate charged particles such as electrons, protons, or ions to a high-energy state at approximately a maximum of several trillion electron volts (several TeV). The accelerator was originally developed for the studies of atomic nuclei and elementary particles. Recently, the application of the accelerator has been extended to a wide range of scientific and technical fields including, for example, very large scale integrated circuits (LSI), microfabrication (lithography), substance studies, and life sciences by using emitted light (referred to as synchrotron orbital radiation (SOR) light) which is generated by the accelerator. When the orbit of electrons propagating in a vacuum substantially at light velocity is bent by a deflecting magnetic field, the emitted light is generated in the tangential direction of the orbit.
The accelerator thus applied in the wide range has a high-frequency acceleration cavity provided at the beam line of a charged particle beam to supplement energy lost for the acceleration of charged particles or lost as the SOR light.
The high-frequency waves fed into the high-frequency acceleration cavity oscillate, and a high electric field is thereby generated. The charged particle beam is accelerated by the high electric field. When the high electric field is thus generated, a circulating current passes through the inner surface of the high-frequency acceleration cavity. This circulating current is a high-frequency current, and therefore runs at a skin depth corresponding to the material of the inner surface of the high-frequency acceleration cavity. As a result, the circulating current leads to Joule loss.
This Joule loss becomes considerable if a high electric field necessary for the acceleration of the charged particle beam is obtained in a normal conducting high-frequency acceleration cavity made of oxygen-free copper or aluminum. A high-power high-frequency oscillator capable of feeding a great amount of high-frequency power is needed to compensate for the Joule loss. However, the output of the high-frequency oscillator is limited, and there are many problems in cooling the high-frequency acceleration cavity which has been heated by the Joule loss. Thus, the application of the normal conducting high-frequency acceleration cavity is limited.
Accordingly, it is known to manufacture a high-frequency acceleration cavity by using a superconducting material much lower in radio-frequency resistance than a normal conducting material in order to reduce a current running through the inner surface of the high-frequency acceleration cavity (see, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2009-135049).
This superconducting high-frequency acceleration cavity is used in various fields. For example, an electron beam accelerator is coming into practical use for an X-ray free electron laser which has recently been constructed in Germany or for international linear colliders which have recently been developed all over the world. Thus, the superconducting high-frequency acceleration cavity is used to obtain electrons having the highest possible energy within the range of limited power and limited space.
However, welding is often used to manufacture such a superconducting high-frequency acceleration cavity. Weld-sputtering of the inner surface of the cavity and the inclusion of an impurity during welding increase the Joule loss, and limit the performance of the high-frequency acceleration cavity. It is therefore preferable to minimize welded portions. One method of manufacturing a superconducting high-frequency acceleration cavity by welding is to weld and thereby bond a plurality of bowl-like superconducting materials which are formed from a plate material, for example, by deep drawing.
In the meantime, one (seamless) manufacturing method that eliminates the welded portions can be to process a cylinder made of a superconducting material into the form of a cavity, for example, by hydraulic molding. Here, one way chosen to create a cylinder is to either round plates and weld the abutted ends of the plates or chip a bulk material. However, the manufacturing method that rounds the plates cannot eliminate the welded portions. The manufacturing method that chips the bulk material, on the other hand, produces a great amount of chips and leads to a cost rise.